1. Field of the Invention
The present invention relates to a liquid crystal display device provided with a liquid crystal panel and a frame for covering the periphery of the display surface of the liquid crystal panel.
2. Description of the Related Art
A liquid crystal display device is usually provided with a backlight, a liquid crystal panel for displaying an image by transmitting light emitted from the backlight, and a frame for covering the periphery and side surfaces of the display surface of the liquid crystal panel. A cushioning member composed of silicone rubber, foam material, or the like is also provided between the liquid crystal panel and the frame in order to prevent light leakage or ingress of debris (see Japanese Laid-Open Patent Application Nos. 9-171173 and 2002-174811, for example).
FIG. 1 is a partial cross-sectional diagram showing a conventional liquid crystal display device. A box-shaped rear frame 2 is provided in this conventional liquid crystal display device 101. The rear frame 2 is composed of a rectangular base panel 2a and four side panels 2b that stand perpendicularly with respect to the surface of the base panel 2a from the edges of the base panel 2a. In the following description, the direction in which the side panels 2b stand as viewed from the base panel 2a is referred to as the forward direction 21, the opposite direction thereof is referred to as the rearward direction 22, and the direction orthogonal to the forward direction 21 and rearward direction 22 is referred to as the lateral direction 23.
A frame-shaped resin chassis 3 is provided inside the rear frame 2. A main body 3a disposed parallel to the side panels 2b of the rear frame 2 is provided to the resin chassis 3. In the plane that includes the lateral direction 23, the main body 3a is elbow-shaped in cross-section, and a groove 3b is formed on the rear surface of the main body 3a. The outer surface of the main body 3a is connected to the inner surfaces of the side panels 2b of the rear frame 2. An extension 3c also extends towards the inside of the frame from the end of the main body 3a on the side of the forward direction 21. The main body 3a and the extension 3c are integrally formed from resin.
An optical waveguide 4 and a lamp (not shown in the drawing) for emitting light are provided inside the resin chassis 3. The lamp and the optical waveguide 4 are held in place by the resin chassis 3. The lamp is positioned at the end inside the resin chassis 3, and is configured so as to emit light to the optical waveguide 4. The optical waveguide 4 is positioned at the center inside the resin chassis 3, and is configured so that light emitted from the lamp enters the side surface thereof, and the light is emitted towards the forward direction 21 from the front surface of the optical waveguide 4. An optical sheet 5 is affixed to the front surface, that is, the light-emitting surface, of the optical waveguide 4. The optical waveguide 4 and the optical sheet 5 are positioned behind the extension 3c of the resin chassis 3, and the peripheral edges of the optical waveguide 4 and the optical sheet 5 are held between the base panel 2a of the rear frame 2 and the extension 3c of the resin chassis 3. The backlight is formed from the lamp, the resin chassis 3, the optical waveguide 4, and the optical sheet 5.
A liquid crystal panel 6 is also provided in front of the extension 3c of the resin chassis 3. As viewed from the forward direction 21, the liquid crystal panel 6, the optical sheet 5, and the optical waveguide 4 are arranged in substantially the same position. The periphery of the rear surface of the liquid crystal panel 6 is attached to the extension 3c of the resin chassis 3 by double-sided tape 51. A silicone spacer is also sometimes provided instead of the double-sided tape 51.
A front frame 7 is also provided so as to cover the front and sides of the rear frame 2. A frame-shaped front panel 7a and four side panels 7b that stand towards the rearward direction 22 from the edges of the front panel 7a are integrally formed in the front frame 7, and an opening 7c is formed in the center of the front panel 7a. The front panel 7a of the front frame 7 is positioned in front of the liquid crystal panel 6, and the side panels 7b are positioned on the outside of the side panels 2b of the rear frame 2. As a result, the front frame 7 covers the periphery of the liquid crystal panel 6, the resin chassis 3, and the side panels 2b of the rear frame 2. The frame 8 is formed from the rear frame 2 and the front frame 7.
A cushioning member 52 is provided between the periphery of the liquid crystal panel 6 and the front panel 7a of the front frame 7. The cushioning member 52 is in contact with both the front surface of the liquid crystal panel 6 and the rear surface of the front panel 7a. The cushioning member 52 is formed from silicone rubber, a foam material, or another material having cushioning properties, and the thickness thereof is about 0.3 to 1.0 mm. The liquid crystal panel 6 is held between the extension 3c of the resin chassis 3 and the front panel 7a of the front frame 7 via the double-sided tape 51 and cushioning member 52, respectively.
In this conventional liquid crystal display device, the cushioning member 52 is provided between the periphery of the liquid crystal panel 6 and the front panel 7a of the front frame 7, whereby debris are prevented from entering the frame 8 from the outside. Prevention of light leakage can also be anticipated by providing the cushioning member 52. The term “light leakage” refers to the effect whereby light emitted from the backlight and transmitted through the liquid crystal panel 6 is diffusely reflected between the liquid crystal panel 6 and the front panel 7a of the front frame 7 and leaked out from the gap between the liquid crystal panel 6 and the front frame 7, and this leaked light is visible to the viewer depending on the angle from which the viewer views the liquid crystal panel 6. Furthermore, in this conventional liquid crystal display device, the liquid crystal panel 6 is bonded to the resin chassis 3 by the double-sided tape 51, whereby debris that have entered the frame 8 are prevented from penetrating between the optical waveguide 4 and the liquid crystal panel 6.
However, the conventional technique described above has such drawbacks as those described below. When there is low precision in the shapes of the members constituting the liquid crystal display device, the gap between the frame and the liquid crystal panel becomes narrow at a part of the frame, the thickness of the cushioning member increases beyond design specifications, and other effects occur, and the cushioning member sometimes exerts an increased load on the liquid crystal panel. Since the liquid crystal panel is bonded to the resin chassis by double-sided tape or a silicone spacer, a continuous load is placed on the liquid crystal panel when either the liquid crystal panel or the resin spacer is warped. Furthermore, when there are rapid changes in the temperature of the environment surrounding the liquid crystal display device, the double-sided tape or silicone spacer shrinks and/or expands and exerts a load on the liquid crystal panel. When a significant physical load is placed on the liquid crystal panel in this manner, display abnormalities occur in the liquid crystal panel. An IPS-type (In Plane Switching: system for switching within a plane) liquid crystal panel is particularly prone to display abnormalities that occur due to a physical load.
Since the space between the frame and the liquid crystal panel must naturally be widened in order to position the cushioning member between the frame and the liquid crystal panel, the thickness of the liquid crystal display device as a whole increases.
The material cost of the liquid crystal display device also increases because of the expensive silicone rubber or foam material used to form the cushioning member.